Ceramic transducer elements



April 18, 1961 J. M. JACQUE CERAMIC TRANSDUCER ELEMENTS Original FiledSept. 10, 1956 INVENTOR BY ATTORN Y 1 2,980,81 1 Ice Patented Ag r 1961CERAMIC TRANSDUCER ELEMENTS James M. 'Jacque, Conneaut, Ohio, assignorto The Astatic Corporation, Conneaut, Ohio, a corporation of OhioOriginal application Sept. 10, 1956, Ser. No. 608,934. Divided and thisapplication Jan. 4, 1960, Ser. No. 311

6 Claims. (Cl. 310-94) This application is a division of my co-pendingapplication, Serial No. 608,934, filed September 10, 1956, which isassigned to the assignee of the present application.

This invention relates generally to the art of converting mechanicalvibrations and movements into proportional electrical signals and hasparticular reference to improvements in the manufacture and design ofceramic piezoelectric transducer elements of the type commonly employedin phonograph apparatus, microphones, ultrasonic apparatus and the like.

Probably the best known type of transducer in commercial use at thepresent time is the Bimorph. This type of electro-mechanical transducerhas opposite faces of active piezo-electric material and is mounted insuch a manner that when a movement is transmitted to the transducer oneof the sides is compressed and the other expanded thereby producing anelectrical signal at its electrodes. In the manufacture of such Bimorphsprior art practice has been to fabricate relatively thin sheets ofceramic piezo-electric material, comprising one of the earth titanates,for example, maturing these sheets at high temperatures in a firingkiln, applying a silver electrode face to the major faces of each of theceramic sheets and again firing the coatedsheets to set the conductiveelectrodes. A metal vane, usually brass, is prepared by tinning bothfaces thereof and carefully prepared chips of the coated and maturedceramic piezo-electric sheets are soldered to this metal vane, one oneach'side thereof. The resultant sandwich is then heated to fuse thevarious elements and polarized according to well known principles toprovide a small commercially acceptable transducer element. It will beappreciated that the multiple steps involved in the above outlinedprocess must be completed with extreme care and precision andconsequently this has resulted in high reject rates and acorrespondingly high cost for such elements.

As an overall object, the present invention seeks to provide an improvedmethod for manufacturing Bimorph transducer elements in a moreexpeditious manner than has heretofore been possible in the prior art.

A further object is the provision of a method for fabricating transducerelements whereby laborious, time consuming and expensive multipleassembly operations are eliminated. This is accomplished in the presentinstance by utilizing extrusion techniques and processing a series ofBimorphs prior to severing them into individual transducer elements.

More specifically, it is the object of the present invention to providea new and novel transducer element of practical design, having improvedphysical and electrical characteristics rendering the element moresuitable for specific intended uses and applications.

These, as well as other objects and advantages of the invention, willbecome more readily apparent upon consideration of the followingspecification and accompanying drawing wherein there is shown anddescribed cer' tain representative embodiments of my invention.

In the drawing:

Figure 1 is a perspective view of an extruded body strip of my new andnovel transducer; and

Figure 2 is a perspective view of a completed individual Bimorphtransducer element constructed in accordance with the teachings of thepresent invention.

Referring now to the drawing, the reference numeral 10 indicatesgenerally an extruded raw body strip which is generally rectangular incross section and comprises a relatively thin top wall 11, a thin bottomwall 12, a left edge wall 13 and a grooved right edge wall 14. Thesewalls enclose a central aperture 15 which extends longitudinally throughthe extruded section of body strip 10.

In accordance with the method of the present invention the body section10 of Figure 1 is extruded in continuous fashion and severed in lengthssuitable for handling in a firing kiln, not shown. After suitablepreliminary drying the body section is fired to bring about ceramicmaturation. Upon removal from the firing kiln, the interior surfaces ofthe aperture 15 are coated with a suitable conductive metal paint 16 andthe top and bottom walls 11 and 12 are coated with relatively narrowstrips of metal paint 17 and 18, respectively, which extend the entirelength of the matured body strip 10. The painted body strip is againreturned to a kiln for setting of the painted portions 16-18 andreducing the same to its final conductive metallic character.

The separate metallizing operation and second firing described above maybe consolidated in a single firing as completely described and claimedin a co-pending patent application of Claude A. Lindquist, Jr., SerialNo. 608,898, filed September 10, 1956, and assigned to the assignee ofthe present invention, wherein a suspension of noble metal, such asplatinum or palladium, is applied directly to the unfired ceramic bodyand is reduced simultaneously with the firing thereof for curing.

The long tubular body section shown in Figure 1 of the drawing, with theceramic material and the metal paint forming the electrodes 16-18 havingbeen properly matured, is next polarized by the application of highvoltage electrical potential. One terminal of polarizing voltage source,not shown, is connected to the inner electrode 16 while the otherterminal is electrically connected with both of the electrodes 17 and18. The electrostatic field generated in the top and bottom walls 11 and12 of the body section create a condition of electrical stress in thesewalls which is retained after removal of the external polarizingpotential source and thus the body section is conditioned to exhibit therequisite piezo-electric characteristics.

The body section 10 is next severed transversely to the direction ofextrusion as along the plurality of broken lines 19 to produce a seriesof small commercially acceptable Bimorphs 20, one of which isillustrated in Figure 2 of the drawing.

A preferred method of utilizing a Bimorph 20 of the present invention asa mechanical-electrical transducer, as in a phonograph pick-up, forexample, is to clamp the rear end of the edge wall 13 between opposedsuitable resilient clamping pads 23 and to apply the mechanical drivingforce through a drive lever 24 which is operative attached to aphonograph needle or stylus, not shown. The edge wall 14 is suitablygrooved as at 25 to accommodate the drive lever 24, which, in thepresent instance, is shown as being a thin rectangular bar.

If an alternating motion is imparted to the drive lever 24 asrepresented by arrow 26 a functional piezo-electric plane of theelement, represented by the broken lines 27, will also move in analternating fashion. This causes alternating opposite stresses oftension and compression in the top wall 11 and the bottom wall 12thereby resulting in a charge of alternating sign on the electrodes 17and 18. It is noted that the functional plane 27 of the Bimorphtransducer is disposed transversely to the extrusion axis of the bodystrip and the physical axis of the individual transducer element. Theelectric charges appearing on the electrodes '17 and 18 are conductedvia suitable "lead wires, not shown, to an associated amplifier forreproduction as audible vibration.

In order to control'the mechanical compliance of the Bimorph transducerelement described above it is possible to fill the elongated aperture 15in the body strip before the same is severed with molten metal orvarious liquid plastics by dipping one end of the tube in such asolution and evacuating the internal aperture to draw the solution intothis portion of the body section. This operation, of course, would becompleted after metallizing of the electrodes but prior to polerizationof the body strip as clearly set forth in the co-pending patentapplication of Charles L. Maxon, Serial No. 469,794, filed November 18,1954-, now abandoned, and in a divisional application thereof, SerialNo. 668,199, filed June 26, 1957, which are assigned to the assignee ofthe present invention.

It should thus be apparent that I have accomplished the objectsinitially set forth by providing a method of fabricating a plurality ofBimorph elements without the laborious operations used in the prior art.All operations, such as applying electrodes, and polarizing, are carriedout prior to the severing of the body stock into individual units whichallows ease of handling and working in an efiicient manner. In addition,the specific Bimorph transducer assembly disclosed herein is welladapted for use in phonograph reproducing systems.

As many changes may be made in the method and transducer disclosed andshown herein, reference should be had to the following appended claimsin determining the scope of my invention.

I claim:

1. A piezo-electric ceramic transducer comprising a tubular sectionhaving top and bottom walls and two end walls, electrode areas on saidtop and bottom walls, means for securely anchoring one of said endwalls, means for applying a driving force to the other of said endwalls, said means for applying a driving force comprising a drive lever,said other end wall being formed with a groove-like recess therein toreceive said drive lever, and the functional piezo-electric axis of saidelement being disposed transversely to the physical axis of said tubularsection.

2. A piezo-electric ceramic transducer of generally rectangular crosssection and having an aperture extending therethrough, said transducerhaving top and bottom walls and two end walls, said top and bottom wallsbeing relatively thinner than said two end walls, the axis ofpiezo-electric action of said transducer being disposed transversely tothe axis of said aperture, means for anchoring one of said end walls,electrode areas on said top and bottom walls, means to apply a drivingforce to the other of said end walls to place said top and bottom wallsin tension and compression, said'means to apply a driving forcecomprising a drive lever, and said other end wall being formed with adepression therein to receive and support said drive lever.

3. A piezo-electric transducer element comprising a tubular section ofpiezo-electric material, electrodes on surface areas of said tubularsection, means for securely anchoring one portion of said transducerelement, means for applying a driving force to another portion of saidtransducer element, said means for applying a driving force comprising acoupling member, and said another portion of said transducer elementhaving a depression therein for receiving and supporting said couplingmember. i

4. A piezo-electric transducer element comprising a mass ofpiezoelectric material, electrodes on surface areas of said mass ofpiezo-electric material, means for securely anchoring one portion ofsaid mass of piezo-electric material, means for applying a driving forceto another, portion of said mass of piezo-electric material, said meansfor applying a driving force comprising a coupling memher, and saidanother portion of said mass of piezoelectric material having adepression therein for receiving and supporting said coupling member.

5. A transducesr element according to claim 4 further characterized inthat said depression comprises an elongated groove, said coupling membercomprising a drive lever, and one end of said drive lever being receivedin said groove.

6. A piezo-electric ceramic transducer of generally rectangular crosssection and having an aperture extending therethrough, said transducerhaving top and bottom walls and two end walls, said top and bottom wallsbeing relatively thinner than said two end walls, the axis ofpiezo-ele'ctric action of said transducer being disposed transversely tothe axis of said aperture, means for anchoring one of said end walls,electrode areas on said top and bottom walls, means to apply a drivingforce to the other of said end walls to place said top and bottom wallsin tension and compression, said means to apply a driving forcecomprising a drive lever, and said other end wall being formed with adepression therein to receive and support said drive lever.

No references cited.

